Repeating a process for a variable of the Observable type containing key-value pairs of strings and Threads

Hi everyone, I'm a new member of this forum and I've been struggling with a problem for the past few days. I am trying to create a loop that will iterate through every object in my collection.

Here is the variable I am working with:

threads: Observable<{ [key: string]: Thread }>;

Below is the function where I am attempting to create a loop using forEach or for:

findById(threadId: string) : Thread {
let foundThread: Thread = null;

this.threads.forEach(
  (thread: Thread): void => {
    if (thread.id === threadId) {
      foundThread = thread;
    }
  },
  null
);
return foundThread;
}

However, I encountered this error:

TS2345:Argument of type '(thread: Thread) => void' is not assignable to parameter of type '(value: { [key: string]: Thread; }) => void'. Types of parameters 'thread' and 'value' are incompatible. Type '{ [key: string]: Thread; }' is not assignable to type 'Thread'. Property 'id' is missing in type '{ [key: string]: Thread; }'

I also tried another solution, but it did not work either:

findById(threadId: string) : Thread {
let foundThread: Thread = null;
for (let thread in this.threads) {
  if (thread.id === threadId) {
    foundThread = thread;
  }
}
return foundThread;
}

Thank you for your assistance :)

//////////////////////////////////////////////////////////////////////////

UPDATE :

Here is a different function that I have:

getThreadFromSubscription(threadId: string): Observable<Thread> {
return this.threads
  .map( (threadDictionary: { [key: string]: Thread }) => {
    for (let key in threadDictionary) {
      if (threadDictionary[key].id == threadId)
        return threadDictionary[key];
    }
  });
}

And here is how I intend to use the value returned by the above function:

addNewMessage(objMessage: any) : void {
objMessage.thread = this.threadService.getThreadFromSubscription(objMessage.id)
  .subscribe ((thread: Thread) => {
    if (objMessage.thread != null) {
      const newMessage = new Message(objMessage);
      this.addMessage(newMessage);
    }
    else {
      const newThread: Thread = new Thread();
    }
  });
}

I would appreciate some clarification on whether my variable 'objMessage.thread' will indeed contain the thread value returned by 'getThreadFromSubscription'. Thank you for your guidance :)

Answer №1

threads is not a traditional data structure like a dictionary or list that can be iterated through. Instead, it functions as a stream of events (an Observable). The events emitted from this stream take the form of a dictionary<string, Thread>.

In essence, what you're implying is that sporadically, a new dictionary will be received from the threads Observable. To process each dictionary as it's emitted, you can use the .map operator on your Observable:

this.threads.map((threadDictionary: { [key: string]: Thread }) => {
    // perform operations on the threadDictionary
});

If you need to iterate through each key within the dictionary, consider using a loop like this:

for (let key in threadDictionary) {
    if (threadDictioanry[key].id == threadId)
        foundThread = threadDictionary[key];
}

Given that threads is an observable, you must subscribe to it somewhere to access its emitted values. You could adjust your function to return an Observable<Thread>, which can then be subscribed to for obtaining the appropriate thread once the original threads stream emits a value:

getThreadFromSubscription(threadId: string): Observable<Thread> {
    return this.threads.map((threadDictionary: { [key: string]: Thread }) => {
        for (let key in threadDictionary) {
            if (threadDictionary[key].id == threadId)
                return threadDictionary[key];
        }
    });
}

To subscribe to this transformation, follow this pattern:

this.getThreadFromSubscription('1').subscribe((thread: Thread) => {
    this.processMyThread(thread);
});

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